If you need to get an iris out of a pot, and can do so without disturbing the roots, anytime is ok. In order to do this I dig a hole the size of the pot, sit the pot firmly in the hole to help shape the soil around it, make sure the potted iris has been thoroughly watered in order to keep the soil in place..... then gently holding the top of the soil in one hand turn the pot over and lift it off the root system. Toss the pot and use my free hand on the root system to keep it in place while I upright the plant and place it in the prepared hole. If I do not think I can successfully transfer the plant to the ground without disturbing the root system I wait until after I see the bloom before relocating the plant. Leaving the iris in the pot overwinter does not seem to do any harm to the plant whatsoever. The ones that do not go totally dormant still will not put on a lot of new growth until spring. Potted irises almost never rot due to great drainage. I keep AB's in pots. The pots are large but with out rain patterns being feast or famine the last few years they would have drowned between periods of drought. I keep some irises in pots always. This allows me to bring them up to the door or walkways when they are in bloom. They seem to thrive. Here is one little guy 'Sun Doll' that loves its tub.
I also grow all of my MDB's in pots. They need more shade in the summer and more cold in the winter. I move them to the north ridge during the cold months and let them freeze. They live in pots here when they will not survive in the soil. I have a wheelbarrow full of pots of miniature irises. A friend calls it my iris mobile home. I can move it to the sun in the spring and then into dappled shade during our scorching summers. I always get spring blooms and have not lost one yet.......... if memory serves.
